Method of producing steel rails



July 20, 1937. .1. JOHNSTON 2,087,346

METHOD OF PRODUCING STEEL RAILS Filed Aug. 21, 1950 wwv ATTORNEYSPatented July 20, 1937 2,087,346 METHOD or PRODUCING STEEL RAILS JohnJohnston, United States Short Hills, N. J., assignor to SteelCorporation, N. 31., a corporation of New Jersey New York,

Application August '21, 1930, Serial No. 476,868 9 Claims. (Cl. 14821.5)

My invention relates to methods of making rails of steel or ferrousmetal and more particularly to methods of controlling the cooling ofbeen rolled.

An object of the invention is to provide a method of controlling thecooling of rails such that the residual lengthwise tensile stresseswhich may occur in the head of finished rails are effectively reduced.

10 In making rails heretofore the rails, after having been rolled from ahot ingot, are permitted to cool by exposure to the atmosphere or tocurrents of air. 'This cooling isfof sufiicient rapidity to obviateundue softening pf the Imetal and to 5 keep the area or space requiredby the rails also falls more rapidly than all while coo 'ng within acommercially practicable and economic limit. The heat is given up by theatmosphere, or to the cooling air currents, from the exposed surface ofthe rail, and immediately heat from the interior of the rail begins topass towards the somewhat cooler surface. This passage the interiortowards the surface of the rail, and this gradient is greater thegreater the rate of cooling and the consequent more rapid transfer ofheat outwards through the cross section of the rail.

The temperature difference between the interior and the surface is alsogreater, the greater the cross-sectional dimension of the rail and thethe rail, such as the web and flanges, in which the ratio of extent ofsurface to volume is greater, in the thicker parts, such as the head, inwhich the ratio of surface to volume is less. These differences are alsogreater the larger the rail. Under the relatively rapid cooling nowusual in practice, the temperature diiference between the inner portionof the .head and the appreciable, particularly in the larger and heavierrails.

Within a temperature range, notably from about 750 C. (1400 F.) to about550 C. (1000 F.) steel undergoes transformations which are accompaniedby a sharp The exact temperature of initiation of these transformationsand the rate at which they proceed towards completion, depend primarilyupon the composition of the steel, but also to some extent upon otherfactors such as the mode and rate of cooling. Because of' thetemperature dltl'erence; through the rail section. alluded to of heatnecessarily in-- volves a drop, or gradient, in temperature from web orflange may 'be quite' increase in its volume.-

- necessarily longer path of shortest travel of the heat. Thetemperature of the thinner parts of" above, the completion of thesetransformations times in different portions of occurs at different therail, being in general latest in those portions furthest away from thesurface. The change in volume accompanying these transformations,therefore, also occurs at different times in different portions of therail; and consequently a series of stresses is set up in the rafl' inthis period of its cooling.

These stresses may, with inappropriately rapid cooling, be soconsiderable as to be potentially dangerous as internal sources ofweakness, particularly in the temperature range before the fulleststrength of the s eel has developed; in any case they set up, in thefinished cold rail, a series of residual stresses which can, byappropriate'means, be observed directly.

Systematic, direct, extended measurement of these residual stresses hasshown that there may be, in the head of the rail, residual longitudinal.I

coupled with similar observations which show how' these residualstresses rail change when the rail is put in actual service, have led meto the belief that the head of a new rail should preferably be as freeas practicable from longitudinal tensile stresses, and that the stressgradient should preferably be uniform and invention comprises themethods described in the following specification.

The various features of the apparatus are illusin the head of theture oftransformation for the particular steel comprising the rail. Theparticular temperature of transformation will vary with any given steelwith respect to the rate of cooling from temperatures above the uppercritical temperature. The rate of heat loss is then restricted, thusmore nearly equalizing the temperature throughout the rail. .The properrate of loss of heat varies with the dimensions of the rails to becooled, andmust be adjusted accordingly. In all cases it should besufllciently slow to enable all parts of the cross section of the railto be within the temperature range .of this transformation atapproximately the same parts of the rail, particularly in the head ofthe rail, to undergo the volume and structure change with a minimum ofstrain and distortion.

The cooling of the rail is continued at this retarded rate for a timeafter it has fallen below the transformation temperature, for example,it may be cooled at this rate to 550 C. (1000 F.) or even lower, thusensuring the substantial completion of the structure and volume changes,and the maximum practicable equalization of such stresses as may havearisen, before the more rapid cooling to atmospheric temperature isresumed. Thereupon the normal, rapid or even an enhanced rate of coolingmay be resumed.

The cooling of the rails may be accomplished in any suitable apparatus.In the apparatus illustrated in the accompanying l are placed onandtransand are moved progressively over the hotbed from one end to theother as indicated by the arrow in Fig. 1. While the rails are on thehotbed they are cooled by currents of air, set up by convection orotherwise, which rise upwardly between and about the rails; The rate orcooling is deter mined primarily or very largely bythe rate of movementof these air currents. When the tem perature of the surface of the railsdrops to about 700 C. (1300 F.) or somewhat lower, they enter a closedchamber I2 having louvres l3 and M in its lower and upper walls tocontrol and limit'the upward passage of air about the rails in thechamber. Flaps l5 and I6 may be provided at the rail entrance and exitopenings of-the chamber.

The position or angle of the louvres l3 and I4 may be individuallyregulated to cool the rails to any rate, within limits, in the criticaltemperature range and immediately subsequent to it. The rails then passunder the flap l8 to the outer atmosphere, whereupon the usual morerapid cooling takes place. The rate of cooling of the rails after theretarded cooling in the chamber l2 has been completed may even beincreased to compensate for the relatively longer time and greater spacerequired for the period of retarded cooling.

'It will be understood, however, that other apparatus may be used in thecarrying on of the method of cooling in my invention and that variousmodifications of the form of the apparatus may be made. One suchmodification is to car y out the retarded and controlled cooling in avertical, enclosed part of the hotbed, so arranged time and to enablethe various rail, equalizing the in the above method the steelcomprising comprises hot iormation, equ

' approximatin that the rails in a horizontal position move up one sideand down on the other, being discharged for final cooling on a hotbed ofthe ordinarytype; in this case again, the flow of air past the coolingrails is controlled by suitable louvres or flaps.

What I claim is:

1. The method of treating rails which comprises heating the rail totemperatures above the critical temperature of the steel comprising therail, cooling the rail to a temperature approximating the transformationtemperature of the steel comprising the rail, equalizing thetemperaturedifierentials in said rail at said temperature and thereafterslowly and uniformly cooling the rail during the period oftransformation and at least to temperatures approximating 550 C.

'2. The method of treating rails which comprises heating the rail totemperatures above the critical temperature of the steel comprising therail, cooling the rail to temperatures below the critical temperaturebut above about the transformation temperature of thesteel comprisingthe temperature differentials in from-said cooling and thereuniiormlycooling the rail said rail resulting after slowly and temperatures atleast approximating 550 C.

3..I'he method of treating rails which comprises heating the rail totemperatures above the critical temperature of the steel comprising therail, cooling the rail to temperatures appro mating 700 C. but nottemperature of the said steel, equalizing the temperature diflerentialsin said rail, slowly and uniformly cooling the railthrough the saidtransformation temperature and" at least to, temperaturesapproximatlng550 C. and thereafter cooling in any convenient manner to normaltemperatures.

. 4. The meth or manufacturing rails which compriseshot worhng the railto the desired final size, cooling the rail to temperaturesapproxiniating the transformation temperature of the rail, equalizingthe temperature diflerentials in said rail slowly and unirormly coolingthe rail through said transformation temperature and to temperaturesapproximating 550 C. and thereafter cooling the rail in any convenientmanner to normal temperatures.

5. The method or manufacturing rails which working the rail to thedesired final size, cooling the rail to a temperature below the criticaltemperature or the steel comprisins the rail but above about thetemperature or transthe temperature diflerentials in said rail, andslowly and uniformly cooling the rail through the said transformationtemperature and to temperatures approximating 550 C. and thereaftercooling in any convenient manner to normal temperatures.

flnal size, the rail to temperatures approximating 700 C. but above thetransformation temperature oi the steel comprising the rail, equalizingthe temperature dlflerentials in the temperatures approximating 550 C.and thereafter cooling in any convenient manner to normal temperatures.

I 7. In the manufacture of steel rails, the method or cooling the hotrolled rails which comprises rapidly cooling the rail to temperaturesthe transformation temperature for the steel composition comprising therail, re-

' through the transformation temperature and to below the transformationtarding the rate of cooling of the rail'during the period oftransformation to obtain a substantially 'orm temperature throughout theheads of said rails and thereafter slowly and uniformly cooling saidrails at least to temperatures approximating 550 C.

-8. In the manufacture of steel rails, the

' method of cooling the hot rolled rails which comprises rapidly coolingthe rail to temperatures approximating the Y transformation temperaturefor the steel composition comprising the rail, retarding the rate ofcooling of the rail during the period of transformation to obtain asubstantially uniform temperature throughout; the heads of said-rails,'slowly and uniformly cooling said rails at least to temperaturesapproximating 550 C.

9. In the manufacture of steel rails, the' method of cooling the hotrolled railswhich comprises cooling the rail at any desired rate to atemperature below the critical temperature but above about thetemperature of transformation of the steel comprising the said rail,equalizing the temperature difierentials in the rail, slowly anduniformly cooling the rail through said 7 transformation temperature ata rate substantially adapted to maintain all parts of the rail duringtransformation at substantially the same temperature, slowly anduniformly cooling the rail to temperatures approximating 550 C. andthereafter cooling the rail at a more rapid rate to atmospherictemperatures.

JOHN JOHNSTON.

